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Humidity

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Humidity

Some people describe humid weather as muggy. When the air is humid, it
has a lot of water vapor in it. Water as a gas in the atmosphere is called
water vapor.

The maximum amount of water vapor that can be in the air depends on the
air temperature. Warmer air can hold more water vapor within it. That’s why the
muggiest days usually happen at the height of summer heat. But as the
temperature goes down, the air can hold less vapor and some of it turns into
liquid water.

The amount of water vapor in the air is called
absolute humidity. The amount of water vapor in the air as compared with the amount
of water that the air could hold is called relative humidity. This amount of
space in air that can hold water changes depending on the temperature and
pressure. For example, on a warm 76°F day, you measure that there is half a
gram of water vapor for each cubic yard of air. At that temperature, air is
able to hold 1 gram of water for each cubic yard of air. So what is the
relative humidity? If the air is able to hold twice the amount of water that it
does hold, then the relative humidity is 50%.

Why are
there water droplets on the grass on a cool summer morning, even though it did
not rain the night before? The water most likely came from water vapor which
formed liquid water droplets when it cooled to the dew point. The dew point is the temperature when water
will start to condense out of the air. When air is saturated as much as
possible with water vapor it is at the dew point. Air that is holding less
vapor than it actually could is below the dew point.